We will investigate the mechanism of iron transport in microbial systems to determine if the mitochondria of eucaryotic microorganisms, such as Ustilago sphaerogena, possess a specific active transport involved in the uptake of natural hydroxamic acid chelates of iron, or siderochromes. We will examine the mechanism by which cells are able to utilize siderochrome iron for heme synthesis. The enzyme, ferrochelatase, will be studied to determine if the ionophore, ferrichrome, can serve as an iron donor when the enzyme functions under anaerobic conditions. We will also investigate the possibility that the iron of siderochromes is released by reduction to the ferrous state in a process coupled with the conversion of porphobilinogen to protoporphyrin. The mechanim of iron transfer in species of Penicillium and Fusarium will be studied. Specifically, we will investigate the enzyme catalyzed exchange of iron from weak chelates, such as citric acid, to membrane bound siderochromes. We will complete our research on the role of aminoacylesterases in iron uptake.